Multiple on-the-fly filtering based on markers' features on leaflet

Question

I would like to filter the markers on my (geojson) layer according to two features: year and type of event, ideally using both filters (year and eventType) as check-boxes without using layerGroup at all. I would like to be able to click on a checkbox and update dynamically the markers by filtering them according to feature.properties.eventType too, in addition to the year displayed, something like

  <input type="checkbox" id="all" name="all" value="all">
  <label for="all">All</label>
  <input type="checkbox" id="funfair" name="funfair" value="newsletter">
  <label for="funfair">Funfair</label>
  <input type="checkbox" id="trade" name="trade" value="trade">
  <label for="trade">Trade</label>
  <input type="checkbox" id="exhibition" name="exhibition" value="exhibition">
  <label for="exhibition">Paid exhibition</label>

etc... which would trigger a

filter: function(feature, layer) {
  return feature.properties.eventType == value-of-checkbox;
}

I have five types of eventType. So, for instance, if 1890 is checked, the map is showing all 1890 events, no matter what kind of event it is (because by default it would show all events). If the user checks the 'funfair' and the 'trade' checkbox, though, I want the map to show only the 1890 events of the funfair and trade kind, and not other kind of events.

This is my complete script, which so far is working fine with filtering by year.

var oldmap = L.tileLayer('address', {
  maxZoom: 12
}),

var modernmap = L.tileLayer('https://api.tiles.mapbox.com/v4/{id}/{z}/{x}/{y}.png?access_token={accessToken}', {
  maxZoom: 12,
  id: 'mapbox.streets',
  accessToken: 'mytoken'
});

var map = L.map('map', {
  center: [40.1857864,-4.5536861],
  zoom: 7,
  layers: [oldmap, modernmap]
});

var baseMaps = {
  "Old map": oldmap,
  "Modern map": modernmap
};

var jsontest = {"type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {
        "type": "Point",
        "coordinates":  [ -16.5471268,28.4136726 ]
      },
      "properties": {
        "Name":"Point1",
        "year":'1892',
        "eventType":"funfair",
        "notes":""
      }
    },
    {
      "type": "Feature",
      "geometry": {
        "type": "Point",
        "coordinates":  [ 2.1753895,41.3767925 ]
      },
      "properties": {
        "Name":"Point2",
        "year":'1890',
        "eventType":"trade demonstration",
        "notes":""
      }
    }
  ]};

var mapLayerGroupsYear = [];

function onEachFeature(feature, layer) {
  var year = mapLayerGroupsYear[feature.properties.year];
  if (year === undefined) {
    year = new L.layerGroup();

    //add the layer to the map
    year.addTo(map);

    //store layer
    mapLayerGroupsYear[feature.properties.year] = year;
  }

  //add the feature to the layer
  year.addLayer(layer);   
}


var myLayer = L.geoJSON(jsontest, {
  onEachFeature: onEachFeature
})

L.control.layers(baseMaps, mapLayerGroupsYear).addTo(map);

I am a beginner with leaflet so please forgive the dumb question, in case it is.

Answer 1

I propose to have <input> checkboxes for both the years and the event types outside the map container. The filter function in the L.GeoJson definition rejects every feature that does not have both the respective checkboxes for its year and for its event type checked.

const geojsonLayer = L.geoJSON(null,{
    filter: (feature) => {
        const isYearChecked = checkboxStates.years.includes(feature.properties.year)
        const isEventTypeChecked = checkboxStates.eventTypes.includes(feature.properties.eventType)
        return isYearChecked && isEventTypeChecked //only true if both are true
    }
}).addTo(map)

Now every time the state of a checkbox changes, all markers are removed, checkboxStates is updated and then data is added again, going through the filter.

for (let input of document.querySelectorAll('input')) {
    //Listen to 'change' event of all inputs
    input.onchange = (e) => {
        geojsonLayer.clearLayers()
        updateCheckboxStates()
        geojsonLayer.addData(jsontest)   
    }
}

The utility function updateCheckboxStates is here. It assumes that the <input> elements have a class of either event-type or year.

function updateCheckboxStates() {
    checkboxStates = {
        years: [],
        eventTypes: []
    }

    for (let input of document.querySelectorAll('input')) {
        if(input.checked) {
            switch (input.className) {
                case 'event-type': checkboxStates.eventTypes.push(input.value); break
                case 'year': checkboxStates.years.push(input.value); break
            }
        }
    }
}

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Here is a working jsfiddle: https://jsfiddle.net/newluck77/rk9v0uyo/

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Edit: And three screenshots comparing behaviour:

All events

Trade demonstrations and events of 1892 excluded

Events of 1892 added again (trade demonstrations stay excluded)